See the latest Air Quality Index for the Louisville Metro Area.
See a video explaining the Air Quality Index.
The air quality index is a number indicating the air quality at a particular time in a particular area. The US EPA developed a uniform, standard index to make it easy to compare air quality in different parts of the country, and to avoid confusion for travelers and people who have moved. This index, formerly called the pollutant standards index (PSI), is now called the air quality index (AQI). In October, 1999, the US EPA revised the index to reflect changes in the National Ambient Air Quality Standards (NAAQS), and to better reflect the health risks associated with poor air quality.
This table shows how the AQI numbers correspond to the EPA descriptor categories and colors for air quality.
| Index Range |
Air Quality Descriptor |
Color |
| 0-50 |
Good |
Green |
| 51-100 |
Moderate |
Yellow |
| 101-150 |
Unhealthy for Sensitive Groups |
Orange |
| 151-200 |
Unhealthy |
Red |
| 201-300 |
Very Unhealthy |
Purple |
| 301-500 |
Hazardous |
Maroon |
"Sensitive groups" are active children and adults as well as people with respiratory disease, such as asthma.
To calculate the air quality index for an area, the monitoring agency first calculates the index for each monitor that measures one of the criteria pollutants ozone, CO, SO2, NO2, PM10 and PM2.5. The index for each pollutant is the highest index among all the monitors for that pollutant in the area. The overall AQI for the area is the highest index among all of the criteria pollutants monitored.
The AQI for each pollutant is scaled according to the NAAQS for that pollutant. In most cases, an AQI of 100 corresponds to the primary standard for that pollutant. PM2.5 is the exception; for PM2.5, an AQI of 100 corresponds to a concentration of 40 micrograms per cubic meter (µg/m3). For ozone, there is a separate AQI for 8-hour averages and 1-hour averages. The one-hour average comes into play only when the AQI for the eight-hour average exceeds 100. For NO2, there is an AQI only above 0.600 parts per million (ppm), a level to which air in the Louisville area never reaches.
APCD's automated air quality reporting system CLAIRE reports the AQI for the metro Louisville area hourly every day. Call (502) 574-3319 to talk to CLAIRE. APCD also reports the AQI to the National Weather Service hourly through an automated system.
Pollen and mold
APCD does not collect data on pollen and mold concentrations. But Family Allergy and Asthma does: See pollen and mold counts.